The average depth of the sea is 3800 m, and the sea occupies 99% of the space in which livings can live. The deep sea occupies 85% of the space, but human beings do not observe even 1% of the deep sea. In addition, the number of species of livings, which are not found on the earth, are estimated as being 10 millions to 30 millions, and only 1.4 thousands of species of livings have been found until now. Most species, which are not found yet, live under the sea. This is reflected by the fact that one new living has been found under the deep sea every two weeks on average for the last 25 years. In addition, as land resources are depleted, the oil production obtained from the deep-sea and gas drilling work is increased every year from 2% in 2002 to 8% in 2009 based on the growth oil production. The oil production obtained from the deep-sea and gas drilling work is expected approximately to 15% based on the growth oil production in 2015. In 2009, Korean ministry of land, transport and maritime affairs and four private enterprises establish “the business group for the development of submarine hydrothermal ore deposit” in 2009, and full-scale commercial development is buckled down in the mine lot of Tonga after 2012. The sea deserves to be hugely explored, and dangerous marine environments do not allow the approach of human beings into the sea. An unmanned underwater robot has been developed as one alternative of the above problem, and has been extensively utilized around the world. In addition, the utilization range of the unmanned underwater robot has been gradually enlarged. Underwater robots may be classified into an unmanned underwater vehicle (UUV), which mainly explores a wide region, and a remotely-operated vehicle (ROV), which performs a near work in a narrower region, according to the roles of the underwater robots. Most underwater robots have used a propeller as a propulsion module. The propeller has been used as an underwater swimmer delivery vehicle, and the theory on the propulsion mechanism of the propeller has been sufficiently established. The efficiency of the propeller is highly shown in a specific field. However, an outer western sea is a special region having the wide range of tide, strong tidal currents, and inferior visibility. Accordingly, there are many difficulties when underwater near works are performed by an underwater robot employing the propulsion scheme of the propeller used for the general purpose. In addition, when the deep sea having sedimentary soil is surveyed with precision, the underwater disturbance is caused due to the play of the propeller.
As underwater robots having a type different from the underwater robot equipped with the propeller, there are underwater robots using a caterpillar and underwater robots having several legs. A lobster robot has been developed as a part of a biomimetic study (Joxkh, A. (2004), “Underwater walking”, Arthropod Structure & Development Vol 33, pp 347-360.). Through the above study, the mechanical structure and the walking of a lobster have been analyzed, and a central controller has been developed based on artificial muscle actuators and command neurons. The robot is focused on the biomimetic recognition and a walking study rather than an actual work. In addition, in order to survey the coastline, an amphibious six-leg walking robot has been studied (Tanaka, T., Sakai, H., Akizono, J. (2004). “Design concept of a prototype amphibious walking robot for automated shore line survey work”, Oceans '04 MTS/IEEE Techno-Ocean '04, pp 834-839.). A waterproof underwater joint has been developed through the robot, and the robot is improved several times and light weighted. However, studies and research are focused on expanding from robots on the ground to underwater robots, so that active studies and research are not achieved in terms of hydromechanics. Meanwhile, land and water robots with six pedals, which are designed to walk and swim by using the pedals, have been developed. However, the land and water robots has a simple structure in which each pedal represents only one degrees of freedom, and not the structure of a robot having multi-legs with multi-joints (Christina, G., Meyer, N., Martin, B., “Simulation of an underwater hexapod robot,” Ocean Engineering, Vol 36, pp 39-47, 2009, Theberge, M. and Dudek, G., “Gone swimming [seagoing robots]”, IEEE spectrum, Vol 43, No 6, pp 38-43, 2006.).
Underwater robots are named unmanned underwater vehicles (UUV), and mainly classified into autonomous underwater vehicles (AUVs) and remotely-operated vehicles (ROVs). The AUV is mainly used for scientific survey or search in a region ranging from several hundred meters to several hundreds kilometers. Most AUVs, which has been developed until now, are utilized for scientific research or a military object. ROVs are utilized for underwater survey or a near work with location precision of several tens centimeters or less. The ROVs are utilized for various works such as the maintenance of underwater pipelines and underwater structures, in addition to the burial of underwater cables.
The applications of the ROVs are summarized as follows. First, the ROV searches for a sunken ship, performs a pulling work, and prevents oil from being spilled from the sunken ship. Second, the ROV performs a marine scientific research, and explores and develops marine resources. Third, the ROV mounts an underwater structure therein, supports the survey of the underwater structure, and performs maintenance of the underwater structure. Fourth, the ROV is utilized for the military purpose such as marine search and marine removal.
The ROV for an underwater work mainly obtains two types of mobility. First, the propeller scheme is effective in a cruising type of vehicle such as the AUV, but does not provide control stability to the ROV performing the near work. This is because hydrodynamic fore is non-linearly applied to the ROV underwater, and the thrust force represents strong non-linearity properties such as a dead zone, a response delay, and saturation. In particular, when the ROV is exposed to the strong sea currents such as the tidal currents of the Korean western sea, the stability in the posture of the ROV and the mobility of the ROV may not be ensured. Accordingly, locating and manipulating with precision are difficult, and a clear ultrasonic image may not be obtained, so that most underwater works may be impossible. The directions of tidal currents are changed four times a day. The maximum flow rate in the Korean western sea reaches the range of three knots to seven knots. In a conventional submarine, a steering work is indispensably instable and high energy consumption is required under the strong tidal current environment.
Second, the caterpillar propulsion scheme does not allow the vehicle to be driven in irregular seafloor topography or a region having obstacles, and the vehicle may disturb the seafloor due to the characteristic of the driving scheme of the vehicle. Since the seafloor always has various obstacles including sunken ships, fisheries, ropes, and wasted nets, and seafloor topography restrictions such as rocks and soft grounds, it is difficult for the vehicle to drive through a caterpillar scheme. In addition, most underwater surveys are in-situ surveys that must be performed while minimizing the disturbance under an environment that the disturbance is not caused. The use of the ROV under the above environment is difficult.
Hereinafter, the technical limitations of the underwater works according to the related art will be summarized again.
Safety
When a diver personally participates in the underwater work, there are various dangerous elements, such as decompression sickness, for the diver.
Working Time
The time in which the diver can work without decompression is limited to 30 minutes at the water depth of 21 m, and to 5 minutes at the water depth of 40 m.
Tidal Current
The directions of tidal currents are changed four times a day. The maximum flow rate in the Korean western sea reaches the range from three knots to seven knots. The tidal current is a dangerous target that it is difficult for the underwater robot as well as the diver to overcome. The conventional submarine using the propeller has controllability that is unavoidably unstable under the strong tidal environments and high energy consumption.
Inferior Visibility
One of characteristics of the Korean western sea is in inferior visibility. Although the visibility varies with regions and times, many regions have the visibility only in the range of 20 cm to 30 cm.
Obstacles and Irregular Seafloor Topography
Various obstacles such as sunken ships, fisheries, ropes, and wasted nets, and seafloor topography restrictions such as rocks always exist, which block the works of the diver and the underwater robot, and even threaten the life of the diver.
Environmental Interference
The underwater robots employ a propeller scheme or a caterpillar scheme unavoidably disturbs the seafloor. Many underwater surveys must be performed under an environment without disturbance.
To overcome the strong tidal currents and the inferior visibility is the big limitation in a technology using a robot (unmanned underwater robot) among conventional underwater work technologies. HEMIRE (having the size of L3.3 m×W1.8 m×H2.2 m) receive the resistance force of about 200 kg at the tidal currents of 2 knots, and a cable having the length of 200 m and the diameter of 20 mm receives the resistance force of about 240 kg. Increasing the thrust to overcome the resistance force increases the total weight and the total size, which cannot fundamentally solve the above problem.